A reciprocating compressor (for example, a high speed reciprocating compressor) is an example of a positive-displacement compressor that uses one or more pistons driven by a crankshaft to deliver working fluids (for example, gases) at high pressure. Generally, the pistons are hollow and have a cavity therein. The reciprocating compressors typically operate to deliver compressed gases having a pressure from about 50 psi to about 2000 psi. Due to this high-pressure operation, gas may enter the cavity of the piston, and the pressure of the gas in the cavity may build over time.
Generally, as per the safety standards set forth by the American Petroleum Institute (API), any chamber or cavity must be vented (for example, to equalize the pressure in the cavity with the outside pressure). In addition, to prevent excessive wear of parts any debris, such as casting sand, grit, debris due to machining, etc., within a chamber or cavity be contained therein and should not exit the cavity. In order to satisfy these requirements, piston valves or plugs are typically installed on an outer surface of the piston to vent the piston cavity by providing a flowpath for the gas in the piston cavity to exit the piston cavity.
FIG. 1A illustrates a cross-sectional view of a conventional piston plug 100. FIG. 1B illustrates a cross-sectional view of a piston 110 in which the piston plug 100 has been installed in a plug hole 128 defined by an outer surface 124 of the piston 110. Referring to FIGS. 1A and 1B, the piston plug 100 has a ball 102 and a spring 104 axially disposed in a through hole 108 axially defined by the piston plug 100. The ball 102 and the spring 104 are secured in the through hole 108 via a fastener 106. The piston 110 is disposed to reciprocate axially in a bore 114 in a cylinder 112. A fluid chamber 116 is formed by the piston 110 and the bore 114. An inner surface 126 of the piston 110 is exposed to the fluid chamber 116. The gas in the fluid chamber 116 may enter the piston cavity 111 from the fluid chamber 116. When installed, a bottom surface 122 of the piston plug 100 is exposed to the piston cavity 111 and a top surface 120 of the piston plug 100 may be flush with the outer surface 124 of the piston 110. When the pressure of the gas in the piston cavity 111 reaches or exceeds a predetermined value, the ball 102 is dislodged from its seat (for example, formed via the shoulder in the through hole 108) and the gas in the piston cavity 111 escapes via the piston plug 100. The through hole 108 provides a straight (collinear) flowpath for the gas in the piston cavity 111 to escape.
Because the through hole 108 of the piston plug 100 forms a flowpath 118 that is straight (collinear), debris inside the piston cavity 111 exits along with the gas in the piston cavity 111. Also, the high-speed, high-pressure operation of the reciprocating compressor may cause frequent breaking of the spring 104. Since the flowpath 118 through the piston plug 100 is collinear and extends along the direction of motion of the piston 110 in the cylinder 112, spring fragments may also exit the piston plug 100 via the through hole 108.
Accordingly, there is a need for a piston plug that vents the piston cavity and also prevents debris from exiting the piston.